This disclosure is directed to toner compositions with improved rheological properties.
Emulsion aggregation (EA) toners are used in forming print and/or xerographic images. Emulsion aggregation techniques typically involve the formation of an emulsion latex of resin particles that have a small size of from, for example, about 5 to about 500 nanometers in diameter, by heating the resin, optionally with solvent if needed, in water, or by making a latex in water using an emulsion polymerization. A colorant dispersion, for example of a pigment dispersed in water, optionally with additional resin, may be separately formed. The colorant dispersion may be added to the emulsion latex mixture, and an aggregating agent or complexing agent may then be added and/or aggregation may otherwise be initiated to form aggregated toner particles. The aggregated toner particles may be heated to enable coalescence/fusing, thereby achieving aggregated, fused toner particles. Exemplary emulsion aggregation toners include acrylate-based toners, such as those based on styrene acrylate toner particles as illustrated in, for example, U.S. Pat. No. 6,120,967, the disclosure of which is totally incorporated herein by reference.
In conventional EA processes, batch processes may be used for preparing toners. Batch processes feature long processing times and consume a great deal of energy. The heating/coalescence process is particularly time and energy intensive, as the entire batch is heated to the desired coalescence temperature and maintained at that temperature for coalescence to occur. For example, in large-scale production of EA toner, increasing the temperature of toner to the desired coalescence temperature and carrying out the coalescence step may take upwards of 10 hours.
Additionally, in a batch process, high jacket temperatures and low fluid velocity at the walls under stirring can lead to fouling of the reactor walls. This necessitates additional down-time in the production cycle to allow for cleaning in order to restore the heat transfer from the jacket to the fluid in the vessel. This additional down-time further increases the total amount of time for running an extended production cycle to allow for cleaning after a set number of batches.
Furthermore, in batch processing, controlling or adjusting the rheology of a toner is difficult. The rheology of toner particles is one factor that determines the interaction between the toner and the fusing subsystem components. The viscosity and elasticity of the particles are known to have an impact on crease area, fix, offset performance, and also image permanence. Not having the right rheology can lead to defects such as streaks, spots, and smudges. These defects may be caused by the toner not adhering to the substrate, toner not melting completely, or toner contaminating the fuser roll, cleaning web, and stripping fingers. Other issues such as poor fix on the media can be observed.
Therefore, there is a need for improved toners with improved rheological properties.